1. Technical Field
The present invention relates to a method of driving plasma display panels used for wall-mounted televisions and large-scale monitors. The invention also relates to plasma display units.
2. Background Art
A typical AC surface-discharge type panel known as plasma display panel (hereinafter referred to as “panel”) comprises a large number of discharge cells formed between a front plate and a rear plate arranged in a confronting manner. The front plate comprises a plurality of display electrode pairs, each consisting of a combination of a scan electrode and a sustain electrode formed in parallel to each other on a front glass substrate, and a dielectric layer and a protective layer overlaid to cover the display electrode pairs. The rear plate comprises a plurality of parallel-oriented data electrodes, a dielectric layer covering the data electrodes, and a plurality of barrier ribs in parallel to the data electrodes, formed one after another on a rear glass substrate. In addition, phosphor layers are formed over the dielectric layer as well as side surfaces of the barrier ribs. The front plate and the rear plate are placed in a confronting arrangement so that the display electrode pairs and the data electrodes crisscross with respect to each other with a space between them, and the plates are then sealed hermetically. The interior, or the discharge space, is filled with discharge gases including, for instance, xenon gas of 5% in a ratio of partial pressure. Discharge cells are thus formed in areas where the display electrode pairs and the data electrodes confront each other. In the panel of the above structure, gas-discharges inside the individual discharge cells generate ultraviolet rays, which in turn excite the individual phosphors of red (R), green (G) and blue (B) colors to cause luminous emission and display color images.
As a method of driving the panel, it is a general practice to use the subfield method, which is to divide a period of one field into a plurality of subfields, and combine selected subfields to be lighted to display gradation. Each subfield consists of a priming period, an addressing period and a sustaining period, wherein a priming discharge is produced during the priming period to create a wall charge necessary for the subsequent addressing operation on the individual electrode. During the addressing period, an address discharge is produced to create a wall charge selectively in a discharge cell to be lighted for display. During the sustaining period, sustaining pulses are applied alternately to the display electrode pair consisting of the scan electrode and the sustain electrode to produce a sustain discharge in the discharge cell where the address discharge was produced to cause luminous emission of the phosphor layer of the corresponding discharge cell for display of an image.
A variety of energy saving techniques have been proposed for plasma display units of this kind to reduce power consumption. In view of the fact that each of the display electrode pairs is regarded as a capacitive load having an inter-electrode capacitance between the electrode pair, there is disclosed a so-called power recovery circuit as one of the techniques to reduce power consumption especially during the sustaining period, wherein a resonance circuit formed of an inductor component is used to produce an L-C resonance between the inductor and the inter-electrode capacitance, recover electric charge accumulated in the inter-electrode capacitance into a power recovery capacitor, and reuse the recovered electric charge to drive the display electrode pairs (refer to patent document 1, for example).
Also disclosed is a new way of driving in the subfield method, which uses a gradually changing voltage waveform to produce a priming discharge, and reduces luminous emission not relevant to the display of gradation to a maximum extent possible to improve the contrast ratio by producing the priming discharge selectively in certain discharge cells where sustain discharges was made (refer to patent document 2, for example).
There is a tendency in recent years toward increase in power consumption of panels due to introduction of a variety of techniques to enhance high brightness in addition to increase in resolution as well as a strong inclination toward larger screens, all of which demand further reduction of power consumption.    Patent Document 1: Japanese Patent Publication, No. H07-109542    Patent Document 2: Japanese Patent Laid-Open Publication, No. 2000-242224